In a large pot of salted boiling water, cook pasta until al dente, rinse under cold water and drain.
In a medium bowl combine mayonnaise, sour cream, milk and Italian dressing mix. Whisk together until smooth, set aside. In a large salad bowl combine cooked and cooled pasta, peas, olives, salami, green onions, celery and parsley.
Mix in dressing last, reserving 1/2 cup.
Let sit over night in fridge. Stir before serving.